From the point of slaughter until the onset of rigor mortis, glycogen present in the muscles of carcasses is metabolized and converted to lactic acid. As lactic acid accumulates, the pH of muscle is gradually decreased. At the time of slaughter, muscle pH in red meat (e.g. bovine) animals is typically in the range of 7.0 to 7.4; however, at the time of onset of rigor mortis, muscle pH has typically dropped to a range of 5.5 to 5.8. The amount of lactic acid produced, and thus the final pH of muscle, is dependent upon the amount of glycogen present in muscle at the time of slaughter. If muscles have low levels of glycogen at slaughter, then they will have a limited capacity to produce lactic acid and consequently have a higher pH at the time of rigor mortis.
In the case of bovine animals, most cattle arrive at slaughter facilities with normal levels of muscle glycogen. In some instances, stressors, such as management practices, weather, feeding, illness or transportation, can result in depleted muscle glycogen levels before slaughter. When such stress occurs, muscles lack the glycogen quantities necessary to reduce the pH of muscles to normal postmortem levels (pH −5.5 to 5.8) and have high final pH's (>6.2). The pH affects many of the characteristics of muscle. For example, higher pHs may allow muscles to retain greater amounts of water, which results in abnormal light scattering properties. The net result is that these animals produce muscles that have a dark burgundy/purple appearance.
Carcasses presenting muscles that are dark in appearance are commonly referred to in the art as “dark-cutting,” “dark-cutters,” or “dark, firm, and dry (DFD).” Currently, dark cutting beef carcasses are identified at the point in the meat preparation process where USDA quality and yield grading occurs. This location is the first point within the process where muscle tissue is cut and exposed (i.e., ribbing between the 12th and 13th rib as prescribed for grading procedures). When a carcass is identified as a dark cutter, it is sorted out from carcasses destined for normal production. Although palatability characteristics and wholesomeness of meat from dark cutting carcasses is not different from meat derived from carcasses presenting a normal red color, dark-cutting carcasses yield meat that commands a substantially lower price than meat from non-dark-cutting carcasses. Consumers identify the appearance of muscles from dark-cutting carcasses as unappealing and unwholesome and consequently strongly discriminate against these products when they are sold via normal retail markets. As such, retailers are unwilling to purchase muscles from dark cutters, forcing packers to merchandise these products at vastly reduced prices. Moreover, meat from dark cutters is not used in fully-cooked and precooked items such as prime rib and roast beef products because the internal color of meat from dark-cutters remains more red than meat from normal carcasses processed in the same manner. This increased redness may lead to consumer perception that these products were not cooked properly and thus limits the use of meat from dark-cutters in cooked meat operations. Thus, there is a need in the art for a method of treating meat from dark-cutting carcasses to ameliorate the dark color.